The present invention provides a novel water-soluble dispersant and process for using such dispersant which aid in the dispersion of polyester fibers during the preparation of a wet-laid nonwoven fiber mat. The water-soluble dispersant comprises: polyethylene glycol in an amount greater than about 80% by weight of the water-soluble dispersant; a phthalic acid ester moiety; and a monomeric glycol, wherein the phthalic acid ester moiety and the monomeric glycol are present in an amount less than about 20% by weight of the water-soluble dispersant.
Various dispersants have been previously used for the purpose of assisting in the dispersion of polyester fibers during the preparation of wet-laid nonwoven fiber mats. These polyester dispersants are typically suspensions of insoluble polymers in water. The conventional dispersants are satisfactory in their application to polyester fiber but have the following disadvantages: (1) manufacture of insoluble dispersants requires the difficult step of preparing a suspension of an insoluble material in water; and (2) due to the insolubility of these dispersants, they are prone to forming troublesome deposits in sheet forming or drying systems.
The following patents and article disclose various dispersing agents used in the dispersion of fibers: U.S. Pat. No. 4,049,491; French Patent No. 2,124,574; U.S. Pat. No. 4,200,488; French Patent No. 2,109,210; German Patent No. 2,056,923 (T. Ashikaga et al.); and Erdelyi, J. et al., "Synthetic Fiber Dispersion and Binder Precipitation in Nonwoven Fabric Production", Papiripai 22, No. 1: 3-8 (1978).
U.S. Pat. No. 4,049,491 discloses a uniform polyester nonwoven fabric prepared by agitating aqueous dispersions containing polyester staple fibers and an acrylic or Triton X (polyethylene glycol alkylaryl ether) dispersing agent at high shear, adding an acrylic thickener to the foamed composition, and piling the composition on a net.
French Patent No. 2,124,574 discloses the production of nonwoven textile fleece on a papermaking machine by suspending the synthetic and/or natural fibers in water containing 0.01-3% of a modified polyglycol ether containing 75-99% hydrophilic segments and 1-25% hydrophobic segments. That is, 400 parts polyamide fibers are suspended in 200 parts water containing 0.5% of the reaction product of polyethylene glycol ether, 65:35 2,4- and 2,6-tolylene diisocyanate, and 2 moles of stearyl isocyanate.
U.S. Pat. No. 4,200,488 discloses a wet papermaking process used for forming a nonwoven fabric containing staple length synthetic fibers, e.g., polyester fibers. A high-shear agitated mixture is formed of the fibers, air, and water, together with a dispersant such as an alkylaryl polyether alcohol.
The Erdelyi article discloses that the manufacture of nonwoven fabrics by the wet process depends on two major conditions, i.e., uniform dispersion of the fibers and uniform deposition of binders. Viscose, polyamide, polyester and PAN fibers were dispersed in dispersants, such as, cationic and oxidized starch, cationic polyamide-polyamine, cationic PEI, Busperse 55, Sterogenol, and NaOH-treated Al sulfate in amounts of 0.1-2.0% based on fiber dry weight.
French Patent No. 2,109,210 discloses an aqueous dispersion for making nonwoven material which consists of: 1000 parts water; 100 parts natural, RC or synthetic fibers; 0.5-50 parts of an unsaturated polyester resin; and a dispersing agent in amounts of as much as 25% with respect to the weight of the resin.
German Patent No. 2,056,923 (T. Ashikaga et al.) discloses a wet process for the manufacture of nonwoven fabrics from a suspension of organic synthetic staple fibers which is characterized by the use of compounds of the polyethylene glycol amine or alkyl amine acetate type as dispersing agents for the fibers.
The following patents describe various polymer compositions which are coated on fibers: Japanese Patent Application No. 88/203875; U.S. Pat. No. 3,557,039 (McIntyre et al.) issued on Jan. 19, 1971; U.S. Pat. No. 3,416,952 (McIntyre et al.) issued on Dec. 17, 1968; and U.S. Pat. No. 4,410,687 (Schimmel et al.) issued Oct. 18, 1983.
Japanese Patent Application No. 88/203875 discloses polyester fibers for wet-laid handsheets in which 0.1 wt. % or more block copolyetherester produced from terephthalic acid, ethylene glycol and polyethylene glycol is deposited onto polyester fiber with a multi-layered profile. The block copolyetherester having a degree of polymerization of 3-10 is produced from terephthalic acid, ethylene glycol and polyethylene glycol with molecular weight of 700-3000 at a level of 0.1-1 mole of ethylene glycol. The block copolyetherester is applied to the tow in the form of an aqueous solution of 2 wt. % concentration and thereafter heat treated for 5 minutes at 140.degree. C., followed by cutting into 5 mm lengths to produce the polyester fibers for the handsheets. The polyester-based binder fibers from the aforementioned polyester fibers and Melty were mixed at an 80:20 weight ratio, followed by agitation dispersion in water at 2500 rpm using a pulp defibrator. This produced handsheets which were dried at 140.degree. C. using a drum type drier and then subjected to heat treatment to produce polyester paper.
U.S. Pat. Nos. 3,557,039 and 3,416,952 disclose the coating of polyester shaped articles with an aqueous dispersion of a block or graft copolymer. The first polymeric constituent contains repeat units of the type used in fiber-forming polyester materials and the second polymeric constituent preferably is a polyoxyethylene chain.
U.S. Pat. No. 4,453,314 discloses pigment dispersants for coatings comprising polyesters containing 40-75% oxyalkylene moieties. A polyester dispersant prepared containing 9.6% pentaerythritol, 18.2% phthalic anhydride, 51.2% polyethylene glycol monomethyl ether, and 21% soya fatty acid; an acrylic latex coating formulation containing 1% of the dispersant gave coatings having no blacking resistance.
The aforementioned patents disclose either water-insoluble dispersants or polymer composition used as fiber coatings neither of which describe or suggest the advantage of using a water-soluble dispersant to aid in the dispersion of polyester fibers during the preparation of a wet-laid nonwoven fiber mat. The water-insoluble dispersants have the added disadvantage of requiring difficult steps in preparing a suspension of an insoluble material in water, and also the disadvantage that their insolubility makes them prone to forming troublesome deposits in sheet forming or drying systems.
The present invention overcomes the above mentioned disadvantages, as well as provides additional advantages which shall become apparent as described below.